A prostate cancer drug developed by Medivation Inc and Astellas Pharma Inc has been approved by the U.S. Food and Drug Administration for treating men whose cancer has stopped responding to hormone therapy and chemotherapy, the agency said on Friday.

The approval of the drug, to be sold under the brand name Xtandi, comes three months ahead of the agency's late-November decision deadline.

Xtandi, or enzalutamide, is one of a new class of drugs known as androgen inhibitors, designed to interfere with the ability of testosterone to bind to prostate cancer cells.